This invention relates to a method and apparatus for identifying an object. More particularly, this invention uses the techniques of moire diffraction interferometry to apply to an object a finely detailed diffraction grating whose exact structure is mapped by diffraction more techniques and recorded for comparison with future readings of the same grating. Used as an identifying mark or tag, a finely detailed grating is unambiguous, difficult to duplicate, or remove and transfer to another item, and, using the apparatus of the present invention, can be read and compared with prior readings with relative ease.
Optical devices are commonly used to read bar code labels affixed to retail goods and to provide input data used by point of sale systems in retail stores and supermarkets to retrieve price data, print customer receipts and update inventory records. Less commonly, optical devices are used to read unique identifiers which track the movement of a particular article, or to provide identification cards for persons given access to valuables, or restricted equipment or areas.
U.S. Pat. Nos. 4,014,602 and 4,400,616 disclose methods for identifying document cards by including holograms containing encoded data, and data which can only be revealed by persons knowing and having the capability of subjecting the card to the correct light source in the correct manner.
U.S. Pat. No. 4,506,914 applies a security seal to protect the contents of a package by thermally imprinting an identifying "fingerprint" into plastic and recording its unique image for future comparison.
U.S. Pat. No. 4,658,147 uses a spectrometer to analyze a retroreflected beam from an identifier with a unique spectral signature.
Each of these methods for applying identification or a tag to a card or object meets minimal requirements for repeatability, resistance to tampering and duplicating, and ease of use. The present invention meets and exceeds those requirements. An identifier or tag produced and authenticated using the techniques of moire interferometry has a high degree of detail and resolution, which discourages counterfeiting by duplication or transfer of the identifier. In addition, using this invention the tag is readily translated into quantitative data, which can be stored and accessed using data processing systems.
It is therefore a primary object of this invention to provide a novel method for applying and authenticating an identifier on an object.
In the accomplishment of the foregoing object, it is another important object of this invention to provide a method for applying and authenticating a truly unique identifier which has such a high degree of detail and resolution that it defies counterfeiting.
It is another important object of this invention to provide a portable apparatus which enables the application and authentication of the identifier by persons having limited training and understanding of moire techniques.
A yet further object of the present invention is to present an apparatus which reduces the structure of the identifier to quantitative data enabling use of data manipulation to minimize distortions during authentication.
Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.